DSM-5 ( Diagnostic and Statistical Manual of Mental Disorders, 5th edition) Reactive Attachment Disorder (RAD) and Disinhibited Social Engagement Disorder (DSED) are rare disorders sharing social difficulties with autism. The DSM-5 and ICD-10 (International Classification of Diseases, 10th revsion) state that RAD/DSED should not be diagnosed in children with autism. The purpose of our study is to determine whether children can meet criteria for both autism and RAD/DSED and to identify specific symptoms discriminating the disorders. Subjects were 486 children with autism and no RAD/DSED and 20 with RAD/DSED, 4-17 years of age. In total, 13 children with RAD/DSED met criteria for autism. Using the Checklist for Autism Spectrum Disorder (CASD), there was no overlap in total scores between the RAD/DSED with autism group (score range = 15-27) versus the RAD/DSED without autism group (range = 7-10 ). The autism with and without RAD/DSED groups did not differ in CASD scores. Nine of the CASD autism symptoms were found only in the autism with and without RAD/DSED groups. Our study demonstrates that children can meet criteria for both autism and RAD/DSED and that the disorders are easily differentiated by the presence of specific autism symptoms. Autism is a neurogenetic disorder, and RAD/DSED results from severe social-emotional maltreatment. Given the different etiologies, there is no reason why a child cannot have both disorders.